1. Technical Field
The present invention relates to a method of repairing a shroud support and a repair apparatus thereof and more particularly to a method of repairing a shroud support and a repair apparatus thereof which are preferably applicable to repair of a weld of the shroud support in a reactor pressure vessel during a in-service period of a nuclear power generation plant.
2. Background Art
A shroud support disposed in a reactor pressure vessel of a nuclear power generation plant includes a shroud support cylinder, a shroud support plate and a plurality of shroud support legs. The welds of the shroud support include many welds such as a weld (H9) between an inner surface of the reactor pressure vessel and a shroud support plate, a weld (H8) between a shroud support cylinder and the shroud support plate, a weld (H10) between the shroud support cylinder and a shroud support leg, a weld (H11) between the inner surface of the reactor pressure vessel and the shroud support leg, and a weld (H7) between the shroud support cylinder and a lower portion of a core shroud 6.
In the respective welds, cracks may be considered to generate and a plurality of cracks may be considered to generate at optional positions through the length of each weld line. In this case, when cracks are generated at a plurality of positions, every time, an apparatus having a structure dependent upon the position is prepared, thus a problem arises from the viewpoint of cost reduction.
Further, when cracks are generated at a plurality of positions, if the apparatus is moved and installed at each position and repair operation is executed, a problem arises similarly from the viewpoint of operation term reduction and operability improvement. At least, the welds (H8 and H9) of the shroud support have a weld line at 360° in the circumference and when cracks are generated in the entire perimeter, the consideration of a repair method capable of repairing continuously for the entire perimeter of each weld line is preferable from the viewpoint of the process, cost, and radiation exposure reduction.
As a maintenance method and apparatus of the shroud support disposed in the reactor pressure vessel of the nuclear power generation plant which are conventionally proposed, there are an operation apparatus and an operation method (see Japanese Patent No. 4585079) of repairing from a lower side of the shroud support plate by a pantograph mechanism from an inside of the core shroud and an intra-reactor repair apparatus having a structure which it is clamped in a plate thickness direction of the shroud support leg and receives reaction force and an intra-reactor repair method (see Japanese Patent No. 4634742).
On the other hand, as a method for changing an access route, an inspection repair maintenance apparatus (see Japanese Patent Laid-Open No. 2001-296386) of the shroud support for passing through the jet pump and repairing a lower portion of the shroud support, a repair system (see Japanese Patent No. 4262450) of a reactor narrow portion for approaching from a side of an annulus portion and repairing an upper portion of the shroud support plate, and an operation apparatus and an operation method (see Japanese Patent No. 4528711) using an underwater traveling vehicle are proposed.